Preparation of fire-extinguishing material by heating dicyandiamide with alkali metal carbonates or bicarbonates

ABSTRACT

Preparation of powdered fire-extinguishing compositions by heating dicyandiamide with alkali metal carbonates or bicarbonates at 160* C.-180* C., preferably in approximately equimolar proportions, and subsequently powdering the products.

United States Patent Inventor Arnold George Cottrell Winnington, EnglandAppl. No. 797,671

Filed Feb. 7, 1969 Patented Sept. 28, 1971 Assignee Imperial ChemicalIndustries Limited London, England Priority Mar. 1, 1968, Mar. 1, 1968Great Britain 10125/68 and 10126/68 PREPARATION OF FIRE-EXTINGUISHINGMATERIAL BY HEATING DICYANDIAMIDE WITH ALKALI METAL CARBONATES ORBICARBONATES 4 Claims, No Drawings U.S.Cl 169/1, 252/2, 252/5, 252/7,260/551 C Int. Cl A62c l/08, A62d l/OO Field of Search 252/2, 4, 5,

Hodgman et al. Handbook of Chemistry and Physics, Chemical RubberPublishing Company, Cleveland, Ohio 1959, pp. 626 & 627

Primary Examiner-John T. Goolkasian Assistant Examiner-D. .l. FritschAttorney-Cushman, Darby & Cushman ABSTRACT: Preparation of powderedfire-extinguishing compositions by heating dicyandiamide with alkalimetal carbonates or bicarbonates at 160 C.180 C., preferably inapproximately equimolar proportions, and subsequently pow dering theproducts.

PREPARATION OF FIRE-EXTINGUISHING MATERIAL BY HEATING DICYANDIAMIDE WITHALKALI METAL CARBONATES OR BICARBONATES This invention relates to novelcompositions of matter having the ability to extinguish flames arisingfrom the combustion of liquid and gaseous fuels such as liquidhydrocarbons, hydrogen, methane, and of solid fuels such as wood, paperand textiles. It relates particularly to compositions obtained byreactions between alkali metal bicarbonates and dieyandiamide, NH=C(NH)NH-CN, and between alkali metal carbonates and dicyandiamide.

When a mixture of dicyandiamide and potassium bicarbonate is heated fromroom temperature to about 200 C. there is evidence that a reactionoccurs at about 160 C. Thus if one heats such a mixture in adifferential thermal analyzer at a rate of 20 C. rise per minute up to200 C. a strong exothermic peak is noticed at 160 C. indicating that areaction or a physical change of some type has occurred, and sincedicyandiamide melts at 207 C. the peak is probably associated with areaction.

Similarly when a mixture of dicyandiamide and potassium carbonate isheated from room temperature to about 200 C. there is evidence that areaction occurs at about 140 C. and 170 C. Thus if one heats such amixture in a differential thermal analyzer at a rate of 20 C. rise perminute up to 200 C. strong exothermic peaks are noticed at 140 C. and170 C. in dicating that a reaction or a physical change of some type hasoccurred.

Reaction products can indeed be obtained by heating a mixture, forexample in approximately equimolar proportions, of dicyandiamide andpotassium bicarbonate, or of dicyandiamide and potassium carbonate at160-180 C. They possess fire-extinguishing properties, particularly whenin the form of finely divided powders that can be projected into flames.For this purpose the mean particle size of the powder is preferably lessthan 70 microns. Similar products are obtained when sodium bicarbonateor carbonate is used in place of potassium bicarbonate or carbonaterespectively.

The invention thus provides a process for making compositions of matterpossessing fireextinguishing properties comprising heating a mixture ofdicyandiamide and an alkali selected from carbonates and bicarbonates ofsodium and potassium at 160 C. to 180C.

The invention also includes the fire-extinguishing compositions ofmatter made by the said process. 1t is not known at present what thechemical structures of the compositions are beyond the evidence frominfrared spectra of the presence of a --COOM group in the molecule whereM represents an atom of potassium or sodium.

EXAMPLE 1 Potassium bicarbonate (100 g.) (1.0 mole) and dicyandiamide(84 g.) 1.0 mole) were mixed, spread in a layer approximately 1 inchdeep on a tray and heated at 168 C.l 70 C. for 2%. hours. After cooling,the product was finely ground to a maximum particle size of 70 microns.

The fire-extinguishing properties of the powder were assessed in anapparatus designed to test the ability of a powder to extinguish a flameof burning combustible gas, for example hydrogen or coal gas. Theapparatus comprises a vertical silica tube approximately 75 cms. longand 2.3 cms. internal diameter open at its upper end and communicatingat its lower via a suitable adapter with a narrower tube connected to anair supply. Passing through the side of the silica tube at a point about68 ems. from the upper end is a tube 104 cms. internal diameterconnected to a supply of coal gas, or hydrogen or other combustible gas.The part of this gas-carrying to be inside the silica tube is bent insuch a way that 3.0 cms. of its length is disposed along the verticalaxis of the silica tube with its open end upwards so that a flame at theopen end will burn centrally and vertically within the silica tube.

Communicating via a side tube with the air supply tube is a U-tube whichcan hold a charge of powdered material. Application of a sudden airpressure to the open end of the U-tube projects the powder into the airsupply tube up which it is carried by the airflow so that it envelopesthe flame of burning gas. Thus one can compare the flame-extinguishingproperties of different powders by measuring the minimum weight of apowder required to extinguish the flame, the other variables, namelyrate of gas flow and airflow, and the air pressure applied to the U-tubebeing ofcourse kept constant.

Using such an apparatus with coal gas as the combustible gas fed at 1.2litres per minute the relative minimum weights of various powderedmaterials having mean particle sizes below 70 microns were approximatelyNaHCO, 3 KHCO, 2 product as described in example 1 1 EXAMPLE 2 Potassiumcarbonate (138 g.) (1.0 mole) and dicyandiamide (84 g.) 1.0 mole) weremixed, spread in a layer approximately 1 inch deep on a tray and heatedat 168 c.l 70 C. for 2% hours. After cooling the product was finelyground to a maximum particle size of 70 microns.

The fire-extinguishing properties of the powder were assessed in theapparatus described in example 1.

Using it as in example 1 with coal gas as the combustible gas fed at 1.2litres per minute the relative minimum weights of various powderedmaterials having mean particle sizes below 70 microns were approximatelyNaHCO, a mice,

product as described in example 2 I What we claim is:

l. A process for making compositions of matter possessingfire-extinguishing properties comprising heating a mixture ofdicyandiamide and an alkali selected from carbonates and bicarbonates ofsodium and potassium at C. to C. wherein the mixture to be heated is inthe solid state.

2. A process as claimed in claim 1 in which the dicyandiamide and alkaliare mixed in approximately equimolar proportions and the reactionproduct is subsequently reduced in particle size to give a powder ofmean particle size less than 70 microns.

3. Powdered compositions of matter possessing fire-extinguishingproperties and made by providing a solid state mixture of dicyandiamideand an alkali selected from carbonates and bicarbonates of sodium andpotassium, heating the mixture at 160 C. to 180 C., cooling the productand powdering it until the mean particle size of the powder is less than70 microns.

4. A method of extinguishing a burning fuel comprising applying to theburning fuel the composition of claim 3.

2. A process as claimed in claim 1 in which the dicyandiamide and alkaliare mixed in approximately equimolar proportions and the reactionproduct is subsequently reduced in particle size to give a powder ofmean particle size less than 70 microns.
 3. Powdered compositions ofmatter possessing fire-extinguishing properties and made by providing asolid state mixture of dicyandiamide and an alkali selected fromcarbonates and bicarbonates of sodium and potassium, heating the mixtureat 160* C. to 180* C., cooling the product and powdering it until themean particle size of the powder is less than 70 microns.
 4. A method ofextinguishing a burning fuel comprising applying to the burning fuel thecomposition of claim 3.